Reflection type single sideband modulator



May 30, 1961 J. c. cAcHERls 2,986,710

REFLECTION TYPE SINGLE SIDEBAND MODULATOR ff g. @ALL/@MY @KQ/ Ma May 30,1961 J. c. cAcHERls 2,986,710

REFLECTION TYPE SINGLE SIDEBAND MODULATOR Original Filed Aug. 27. 1953 4Sheets-Sheet 2 LINEA POLARIZA N E b F/G. 3 r PRIOR Anf 1r 90 b cowCIRCULAR PoLARlzATIoN C W CIRCULAR POLARIZATION POLARIZATION IN VENTORJOHN C. CACHE/WS May 30, 1961 J. c. cAcHERls 2,986,710

REFLECTION TYPE SINGLE SIDEBAND MODULATOR Original Filed Aug. 27. 1953 4Sheets-Sheet 3 E LINEAR a b PoLAmzATloN A50 l Cow CIRCULAR PoLARlzA-noNy 2 2l P2 Cw CIRCULAR PCLARlzATloN F/G 7 May 30, 1961 Original FiledAug. 27, 1953 RELATIVE PHASE SHIFT IN DEGREES J. C. CACHERIS REFLECTIONTYPE SINGLE SIDEBAND MODULATOR 4 Sheets-Sheet 4 INVENTOR JOHN 0.CACHE/WS BY G! WMWL M REFLECTION TYPE SINGLE SIDEBAND MODULATOR John C.Cacheris, Bethesda, Md., assignor to the United States of America asrepresented by the Secretary bf the Army Original application Aug. 27,1953, Ser. No. 377,004. Divided and this application Apr. 9, 1958, Ser.No. 727,509

Z Claims. (Cl. 332-51) (Granted under Title 35, UJS. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment to meof any royalty thereon.

This invention relates to single sideband modulators in general, andmore particularly to a single sideband modulator of the reflection type.

The present invention is a division of copending application Serial No.377,004 filed August 27, 1953, now abandoned, entitled Single SidebandMicrowave Mod-ulator Using Ferrites in the name of John C. Cacheris.

One object of this invention is to provide an improved microwave singlesideband modulator.

Another object is to provide a single sideband modulator for microwaveswherein high frequency shift of the microwave carrier is obtained.

A further object of the invention is to provide a single sidebandmodulator employing a ferrite in combination with a transverse rotatingmagnetic field to obtain a frequency shift of the microwave carrier.

The specific nature of the invention, as well as other objects, uses,and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawing, in which:

Figure 1 is a schematic diagram of a conventional waveguide half-wavedifferential phase-shift section.

Figure 2 is a perspective view of the differential phaseshift sectionincorporated in the invention.

Figure 3 is a schematic diagram of a conventional single sidebandmodulator for microwave signals.

Figure 4 is a perspective view of one embodiment of the invention.

Figure 5 is a fragmentary cross sectional view showing the mounting ofthe ferrite in a waveguide section.

Figure 6 is a perspective view of another embodiment of the singlesideband modulator of the invention.

Figure 7 is a schematic diagram of the operation of the single sidebandmodulator illustrated in Figures 4 and 6.

Figure 8 is a fragmentary view illustrating another means for creating arotating transverse magnetic field about t-he half-wave sectioncontaining the ferrite.

Figure 9 is a wiring diagram of the rotating transverse magnetic fieldproducing means of Figure 8.

IFigure 10 is a cross sectional view of an improved form of the singlesideband modulator Yof the invention comprising a reflection system.

Figure 1l is a graph showing the relative phase-shift of the microwavein the reflection system of Figure 10 as a function of the appliedmagnetic field. 6 H is the phaseshift obtained when the magnetic vectorof the microwave is parallel to magnetic field transverse to thedirection of propagation and the ferrite element. -is the phase-shiftobtained when the said magnetic vector is perpendicular to the magneticfield. A0 is the differential phase-shift obtained and is equal to 0 n-0 Figure 1 schematically shows a conventional waveguide half-wavesection whereby rotation of polarization 'of a dominant wave isobtained. The waveguide section indicated by 1 having a dielectric slab2 extending United States Patent 2,986,710 Patented May 30, 14961internally therethrough. A linearly polarized wave` represented by thevector E introduced Ifrom the left 'of waveguide section and polarizedat angle 0 to the Xaiis of the section has two mutually perpendicularcmpone'ts represented by vectors a and bj The component alfalng the Xaxis is retarded 180 with respect to component b, along the Y axis.Therefore as the wave emerges from the section, a lags b' by 180 or onehalf wavelength. At the position of b the X axis component will bepointed in the opposite position from a' as indicated by a. VVVeotoraddition of the components a" and b' will give the resultant linearlypolarized wave E polarized at angle 0 clockwise from the Y axis.Therefore the effect of a half-wave differential phase-shift section isto cause a rotation of the angle of polarization in the directionof Yaxis by 26, that is, the section will cause a rotation of the angle ofpolarization at twice the angle of input polarization and in theopposite direction.

In Figure 2 there is shown the differential phase-shift section which isincorporated in the invention wherein a linearly polarized dominant waveis caused to travel through the waveguide section 3 whereby rotation ofthe polarization of the dominant wave and a differential phase-shiftbetween the two components of the dominant wave is obtained through the-use of a ferrite 4 positioned in the waveguide intermediate its endsand subjected to a transverse magnetic field as indicated by the arrowV5. The waveguide section 3 comprises a plastic tubular member 3aprovided with a silvered inner surface 3b. The position of theintroduced wave and emergent wave and components are indicated bythevectors shown at each end of the waveguide and are identical to thoseshown in Figure 1. v

Ferrites are ferromagnetic dielectrics having a resistivity intermediatebetween that of metallic alloys and that of good electrical insulatingmaterials. Because of their high resistivity, ferrites propagatemicrowaves with relative ease and their magnetic properties may bevaried by an applied D.C. field.

, The theory of the behavior of a saturated ferromagnetic material suchas a ferrite magnetizedV in an varbitrary direction with respect to thedirecion of propagation shows that an infinitely large ferromagneticmedium which is homogeneously magnetized in the Y-direction becomesdoubly refracting when plane electromagnetic waves are propagated in theZ-direction. For two linearly polarized waves with H-vectors paralleland perpendicular to the lapplied magnetic field, the indices ofrefraction are given 2 E (ML- a2) y K 7J. l, i If damping andcrystal-anisotyopic field are ignored,

e is the dielectric constant of the medium 'y is the gyromagnetic ratioofthe'electron and zcel: 72B-w2 7.L 72H8 Be.. wz 'Ihe effectivepermeability of the wave whose H-vector is parallel to the D.C. fieldH,a is one since 172=;ie. lt is independent of the magnitude Ha. Theeffective permeability of the wave whose H-vector is perpendicular toApi' =H,B,- 212,2 l [1 Therefore the differential phase-shift of thewave with its magnetic vector parallel to Ha, with respect to the wavewhose magnetic vector is perpendicular to Ha, is

` given by waterway-fi MnammPaL-wrm] Although the theory has beenderived for a saturated infinite medium with no losses, it appears thatthe analysis approximates the waveguide case since double refraction hasbeen observed experimentally. Frequency shifts of a few hundred cyclesper second of a microwave carrier have been accomplished by means ofdifferential half-wave phase-shift section rotated bel tween twostationary quarter-wave differential phase-shift sections of circularwaveguide as schematically shown in Figure 3 wherein I and III indicatedthe quarter-wave differential phase-shift sections (A 90) and IIindicates the half-wave differential phase-shift section (A 180).Section I is oriented at 45 with respect to the electric vector E of themicrowave from the rectangular Wave giude t(not shown). 'Ihe input tosection I which is a linearly polarized microwave may be resolved intoequal orthogonal components as indicated by vectors a and b. Component aparallel to the A axis travels faster than the component b parallel tothe B axis which is delayed by a thin dielectric strip 5 so that the twocomponents have a differential phase-shift of 90. The output of sectionI consists of the two vectors a and b in quadrature in space and time.This emerging signal is a circularly polarized wave which is rotating atmicrowave frequency, the direction of rotation is from the leading tothe lagging component or clockwise as indicated by the arrow 6. SectionII is a half-wave `differential phase-shift section which delays theb-component by an angle of 180, as described in connection with Figurel. Therefore, at the output of Section II, the direction of rotation ofthe circular node will be reversed as indicated by the counterclockwisearrow 7. If the rotating circularly polarized input wave to section IIis considered stationary and if this section is rotated clockwisethrough an angle of the emerging wave is rotated through an angle ofThus the output rotates through twice the angle of rotation of sectionII. Section III is a quarter-wave differential phase-shift section whichreconverts the counterclockwiserotating circularly polarized waves tolinearly polarized wave. The dielectric strips of section II and III areindicated by reference numerals 8 and 9, respectively. To summarize,section I converts the incident linearly polarized waves into circularlypolarized wave. Section 1I rotates the instantaneous orientation of thecircularly polarized waves and thereby shifts the phase of the outputthereof. Section III reconverts the circularly polarized waves tolinearly polarized waves. Furthermore, continuous mechanical rotation ofsection II at a constant speed will produce a continuous change in phasewhich causes a fixed increase or decrease in the frequency of thetransmitted waves as indicated in Figure 3 by FiZn where n is the numberof revolutions per second of section II.

Single sideband modulators of this type have the disadvantage incurredby the mechanical rotation of the half-wave section which limits thefrequency shift to approximately 200 c.p.s. whereas the sidebandmodulator of the invention employing ferrite material in the halfwavesection produces frequency shifts of the order of 20 kc. in transmissionthrough the phase changer without appreciable loss of power.

Figure 4 shows a form which my invention may take. The same generalconfiguration as employed by prior art is used, namely two quarter-wivedifferential phaseshift sections (A 90) 10 and 11 and a half-wavedifferential phase-shift section (A 180) 12. The section 12 contains aferrite 21 positioned intermediate its ends. A two pole winding 15,energized by direct current, creates a magnetic field transverse to thedirection of wave propagation in the section 3. The two pole winding ismounted on a ring 14 which is rotatably mounted by means of bearings inhousing 15 and rotated about seotion 12 by means of a friction disk 16in contact with ring 14 through the groove '17 in the housing. The diskis driven by motor 18. The half-wave differential phaseshift section 12comprises a waveguide made of linen 19 with a thin coating of silver 20on the interior surface thereof as shown in the fragmentary view, Figure5. For the purpose of illustration the waveguide sections are shownsupported on a base 24 by means of arms 25 to 28 inclusive, and also thehousing 15. A disk shaped ferrite 21 is shown afiixed within member 12,although a ferrite of any geometric configuration may be used. Thesilver coating is suicient to carry microwave propagation through theguide, but does not cause large eddy currents usually experienced byrotating a magnetic field through a copper guide. Therectangular-to-round waveguide transitions 36 and 37 couples themodulator to the microwave transmission system in which it is used.Current is provided the winding 13 through slip rings 22 and 23. Thewinding is arranged so that the ferrite in the waveguide section is inalignment with the winding. The rotating transverse magnetic field iscreated when the two pole winding 13 mounted on ring 14 is energized bydirect current and the ring 14 rotated through means of motor 18 aboutthe portion of the half-wave section 12 containing the ferrite 21 whichbecomes double refracting when subjected to a magnetic field.A Thecombination of the double retracting ferrite and waveguide with thetransverse rotating magnetic field produces a continuous change in phasewhich is the equivalent to a frequency shift.

In Figure 7 is shown a schematic diagram of the op- Y eration of thesingle sideband modulator illustrated in Figures 4 and 6 wherein thewaveguide sections thereof are indicated by the reference numerals 10,11 and 12.

The quarter-wave section 10 converts the incident linearly polarizedwave into circularly polarized waves. Section 12 contains the ferrite 21with a rotating transverse magnetic field Ha thereabout adjusted forISO-degree differential phase-shift therethrough and section 11reconverts the circularly polarized waves to linearly polarized waves.The effect of continuous rotating7 of section 12 by means of therotating transverse magnetic fiel-d in combination with the ferrite willcause a fixed increase or decrease in the frequency of the circularlypolarized microwave therein. The plane-polarized wave fed into section10 emerges circularly polarized in, say, a clockwise direction. Hence,the vector E in the plane P1 performs f rotations per second, f beingthe carrier frequency of the incoming energy. If an observer werelocated in section 12 and if section v12 rotates counterclockwise, theobserver will see a frequency f+n, n being the number of revolutions persecond of section 12. Due to the action of section 12, the observer willsee f-I-n counterclockwise rotations of the E vector in the plane P2.Since section 12 itself rotates, that is the rotating transversemagnetic field about produces the effect of rotating section 12, thevector E in plane P2 as seen from section 11 rotates f-l-Zn times asecond. Energy with a frequency f-l-Zn, therefore, emerges from thedevice.

Figure 6 illustrates another yway of `creating a rotating transversefield about section 12 containing the ferrite which comprises athree-phase Winding 30 which when excited will produce a transversemagnetic field that rotates with speed dependent upon the frequency ofthe excitation source. The advantage to the use of this means ofproducing a rotating transverse field about section 12 is that the lackof moving parts greatly extends the upper limits of frequency shiftpossible in the device. The three-.phase winding 30 is mounted inhousing 31 affixed to base 24.

Another means for obtaining a transverse rotating eld about section 12is illustrated in Figure 8 wherein two pairs of coils 32 and 33 aredisposed at right angles to each other about that portion of section 12containing the ferrite in a frame 34 and excited by a 10 kc. generator`as schematically shown in Figure 9. As before, the

field applied to the ferrite is adjusted for a ISG-degree differentialphase-shift and is electrically rotated at kc./sec. by the two pairs ofcoils 32 and 33, 90-degree out of phase. In Figure 9 the 10 kc.generator is indicated by 34 feeding the pair of coils 32 and the pairof coils 33, 90 out of phase through means of the phase changer 33.

An improved embodiment of the invention is shown in Figure 10 whereinthe single sideband modulator for shifting the frequency, F, of themicrowave introduced therein comprises a waveguide differentialphase-shift section (A 90-degree) 40, coupled to a second differentialphase-shift section (A 90-degree) 41. Section 40 is a typical A90-degree section comprising a metallic waveguide member 40a havingaffixed therein a dielectric member 40b. Section 41, however, comprisesa linen cylindrical member 43 provided with a coating of silver 42 onthe inside surface thereof. One end has affixed thereto an electricalshort circuit member 44 which may be in the form of a metallic disk 44soldered to the end or if desired the short circuit member may comprisethe disk 44 mounted on a threaded rod and adapted to be adjustablyextended into the interior of member 43 in engagement with the silvercoating 42. A Teon disk 45 positioned in section 41 intermediate theends thereof supports a ferrite rod 46. However, it is to be noted thata ferrite member of any geometrical configuration may be used in myinvention. The numerals 32 and 34 represent the rotating magnetic fieldstructure shown in Figure 8. The strength of the magnetic field ischosen so that section 41 provides a 90degree differential phase-shift.In operation a linear polarized microwave of frequency F is introducedinto A -degree section 40 with its electric vector oriented at angle 45to the dielectric member 40a, so that the linearly polarized wave willbe converted to a circularly polarized wave at the output of section 40.This circularly polarized wave then travels through section 41, passingthrough the ferrite rod 46 whereby a 90-degree phase differential isobtained. The short circuit 44 reflects the circularly polarized waveand causes it to travel back through section 41 in the oppositedirection through the ferrite rod 46 whereby another 90-degreedifferential phase-shift is obtained, resulting in a total ISO-degreedifferential phase-shift which is equivalen-t to a frequency shift ofthe microwave. This circularly polarized wave then passes back through A90degree section 40 wherein it is reconverted to a linearly polarizedwave having a frequency of FiZn, n being the revolutions per second ofthe rotating magnetic field.

It will be apparent that the embodiments shown are only exemplary andthat various modications can be made in construction and arrangementwith the scope of my invention as defined in the appended claims.

I claim as my invention:

1. An improved single sideband modulator comprising in combination: a90-degree differential phase-shift section having a rst end and a secondend, means applying a microwave signal of frequency f to said first end,a circular waveguide section having one end coupled to the second end ofsaid 90-degree section, shorting means at the other end of said circularwaveguide section, a ferrite member positioned intermediate the ends ofsaid circular waveguide section, a housing having a multiphase windingpositioned about said circular waveguideY so that a rotating transversemagnetic field is applied to said ferrite member when said multiphasewinding is excited, the strength of said magnetic eld being chosen sothat said microwave signal after passing through said ferrite member andbeing reflected by said shorting means back through said ferrite memberin the opposite direction will have received a total -degreedifferential phase-shift, whereupon the microwave signal then passesinto said second end of said 90-degree differential phaseshift section,the microwave signal obtained at said rst end of said 90-degreedifferential phase-shift section thus having a `frequency of f+2n wheren is the speed of rotation of said magnetic field.

2. The invention in accordance with claim l, wherein said circularwaveguide section comprises a non-metallic member having a metallicsurface on the interior thereof, and wherein said ferrite member is aferrite rod concentrically affixed in said circular waveguide section.

References Cited in the file of this patent UNITED STATES PATENTS2,532,157 Evans Nov. '128, 1950 2,769,960 Mumford Nov. 6, 1956 2,787,765Fox Apr. 2, 1957 2,832,054 Fox Apr. 22, 1958 2,891,224 Fox June 16, 1959

